86
Chitinases can be further classified into six different classes (Iseli et al. 1996).
The grouping is based on N-terminal sequence, inducers, signal peptide, isoelectric
point and the enzyme location. Class I chitinases are located in vacuoles. Signal
peptides show high valine content and N terminal has high cysteine content (Flach
et al. 1992). This class has two subdivisions, basic (Ia) and acidic (Ib) chitinases,
and both are reported from plants with an intracellular action. The class II chitinases
are of plant, fungal and bacterial origin and secreted extracellularly. Sequence similarity is observed between Class I and Class II chitinases but class II lack the
cysteine- rich N- terminal. Class III do not show any sequence similarity with class
I and class II. Class IV chitinases are smaller in size (Collinge et al. 1993). A few
examples of classes V and VI are reported (Iseli et al. 1996). The various chitinaseproducing biocontrol agents and the pathogens affected are detailed in Table 3.2.
3.4.2 β-Glucanase
β-glucans, made up of β-linked glucose residues, are important structural components in the fungal cell walls and contribute to rigidity and offer protection (Stone
and Clarke 1992). Enzymes such as β-1,3-glucanase act against β-1,3-glucosidic
linkages and hence can disrupt the fungal cell wall. β-1,3-glucanase production has
Table 3.2 Chitinases producing biocontrol agents against plant pathogens
Sl.
No. Biocontrol agents
Pathogens
References
1.
Streptomyces lydicus
Pythium and Aphanomyces
Mahadevan and
Crawford (1997)
2.
Trichoderma
harzianum
Crinipellis perniciosa
De Macro et al. (2000)
3.
Serratia marcescens
Sclerotium rolfsii
Ordentlich et al. (1988)
4.
Serratia plymuthica
Bothrytis cinerea and Sclerotinia
sclerotiorum
Kamensky et al. (2003)
5.
Pseudomonas sp.
Colletotrichum falcatum
Viswanathan et al.
(2003)
6.
Aeromonas caviae
Rhizoctonia solani and Fusarium
oxysporum and Sclerotium rolfsii
Inbar and Chet (1991)
7.
Arthrobacter sp.
Fusarium oxysporum
Sneh (1981)
8.
Bacillus cereus
Rhizoctonia solani
Pleban et al. (1997)
9.
Enterobacter
agglomerans
Rhizoctonia solani
Chernin et al. (1995)
10.
Paenibacillus
illinoisensi
Rhizoctonia solani
Jung et al. (2003)
I.C. Nair and K. Jayachandran
Chitinases can be further classified into six different classes (Iseli et al. 1996).
The grouping is based on N-terminal sequence, inducers, signal peptide, isoelectric
point and the enzyme location. Class I chitinases are located in vacuoles. Signal
peptides show high valine content and N terminal has high cysteine content (Flach
et al. 1992). This class has two subdivisions, basic (Ia) and acidic (Ib) chitinases,
and both are reported from plants with an intracellular action. The class II chitinases
are of plant, fungal and bacterial origin and secreted extracellularly. Sequence similarity is observed between Class I and Class II chitinases but class II lack the
cysteine- rich N- terminal. Class III do not show any sequence similarity with class
I and class II. Class IV chitinases are smaller in size (Collinge et al. 1993). A few
examples of classes V and VI are reported (Iseli et al. 1996). The various chitinaseproducing biocontrol agents and the pathogens affected are detailed in Table 3.2.
3.4.2 β-Glucanase
β-glucans, made up of β-linked glucose residues, are important structural components in the fungal cell walls and contribute to rigidity and offer protection (Stone
and Clarke 1992). Enzymes such as β-1,3-glucanase act against β-1,3-glucosidic
linkages and hence can disrupt the fungal cell wall. β-1,3-glucanase production has
Table 3.2 Chitinases producing biocontrol agents against plant pathogens
Sl.
No. Biocontrol agents
Pathogens
References
1.
Streptomyces lydicus
Pythium and Aphanomyces
Mahadevan and
Crawford (1997)
2.
Trichoderma
harzianum
Crinipellis perniciosa
De Macro et al. (2000)
3.
Serratia marcescens
Sclerotium rolfsii
Ordentlich et al. (1988)
4.
Serratia plymuthica
Bothrytis cinerea and Sclerotinia
sclerotiorum
Kamensky et al. (2003)
5.
Pseudomonas sp.
Colletotrichum falcatum
Viswanathan et al.
(2003)
6.
Aeromonas caviae
Rhizoctonia solani and Fusarium
oxysporum and Sclerotium rolfsii
Inbar and Chet (1991)
7.
Arthrobacter sp.
Fusarium oxysporum
Sneh (1981)
8.
Bacillus cereus
Rhizoctonia solani
Pleban et al. (1997)
9.
Enterobacter
agglomerans
Rhizoctonia solani
Chernin et al. (1995)
10.
Paenibacillus
illinoisensi
Rhizoctonia solani
Jung et al. (2003)
I.C. Nair and K. Jayachandran